1. Field of the Invention
The present invention relates to a floating multi-unit structure for performing various operations offshore, on lakes, rivers, etc., comprising an operative unit and a support unit releasably pivotably connectable to said operative unit.
2. Description of the Related Art
An example of a floating multi-unit structure of the above type can be found in GB-A-2 108 43 6, where the operative unit and support unit respectively consist of a barge equipped with means necessary to perform the intended operation and a pusher boat or vessel equipped with propulsive means for the interconnected units.
A main object of the present invention is to provide a system consisting of co-operating floating units configured in a manner to permit simple, rapid and economical displacement and/or operation of one or more operative vessels, at maximum personnel safety, while being highly flexible, i.e. suitable for use in a wide range of operational activities.
According to the present application such object is achieved with a floating multi-unit structure of the introductorily mentioned type, in which the support unit, apart from being equipped with propulsion means for the interconnected multi-unit structure, is also equipped with means (at least one unit) to synergetically support the operative unit in performing the intended operation.
Thus, according to the invention, the operative unit is a basic unit generally common to all of the intended operations to be performed, since it is adapted to be equipped with standardized operational equipment for a particular operation, such as offshore drilling and/or production and/or processing hydrocarbons, pipe laying operations etc, while the propulsion/support vessels are substantially of the same standard construction and configuration adapted for various operations to be performed by the main operative unit.
The term xe2x80x9cbasic unitxe2x80x9d, as used herein, should not be interpreted to mean that it merely refers to one single basic configuration. It lies within the scope of the invention to use a plurality of basic units of different configurations. Also contemplated are propulsion/support vessels of somewhat different configurations and sizes. The important aspect of the invention is the fact that by means of a limited number of prefabricated units it will be possible to build up vessels that can do a wide range ofjobs under widely different operational conditions.
The structure or system of the invention is configured in a manner to permit connection between its various members at an offshore location, at wave heights up to 3 meters while permitting disconnection also at larger wave heights and under all kind of weather.
The operative unit would normally be configured as a barge having a small number of standard configurations adapted to different operations.
Thus, the system according to the invention is built up around the combination of propulsion/support vessels and operative barges carrying equipment adapted to the particular operations. The propulsion/support vessels serve purposes beyond that of transporting a barge to the site of operation. Thus, apart from propulsion machinery the vessels are to be equipped so as to assist in the work done by the barge. The vessel-barge connecting portions are standardized in such a manner that the propulsion/support vessels are capable of being flexibly adapted to different needs and jobs.
For instance, it is contemplated that propulsion/support vessels are combined with a barge provided with drilling equipment, resulting in a drilling ship that can lie on DP (dynamic positioning). If a pipe laying vessel provided with DP is desirable, then the propulsion/support vessels are combined with a pipe laying barge. If instead, there is a need for a buoy-anchored production ship, then it might suffice to combine a production barge with one propulsion/support vessel. In those cases where the barge is anchored, it is contemplated that the propulsion/support vessel is disconnected from the barge from time to time in order to perform various operations that otherwise would have to be performed by other vessels.
By configuringamodular drilling-pipelayingunit (or alternatively aproduction unit) as described above, the highest DP class can be achieved with support vessels each having a lower DP class. The highest DP class is normally required, for instance, in connection with sensitive operations such as drilling and production.
The system uses a small number of standardized sizes for the propulsion/support vessels. The connecting equipment is standardized for all of the propulsion/support vessels and barges within each size category in question, in a manner to provide complete connection comparability.
The interconnection between the various members of the main units of the floating structure or system of the invention is carried out by means of a locking device permitting the vessels to have different draughts and further permitting them to move vertically relative to each other, resulting in reduced transfer forces. The locking device, therefore, is important in order to have the system work. It should be strongly pointed out, however, that the locking device is not the central aspect of the system, rather, it is the versatile use of propulsion/support vessels combined with operatively adapted barges that is the essential part of the invention.
Thus, when the system according to the invention is to be used in connection with the production of hydrocarbons offshore, the living quarter module, among other things, could be localized onboard a propulsion/support vessel which is positioned in a manner to be protected from possible fire, gas outburst, etc. on the main unit, i.e. the barge, carrying the production/drilling equipment. For the drilling variant there would be no need for disconnection, the purpose being that the same propulsion/support vessel could be used for productionxe2x80x94as well as for the drilling unit. The system is also contemplated to be established for offshore structures for pipe laying, etc.
In connection with the production of hydrocarbons, for example, the propulsion/support vessel would be prepared for quick disconnection from the barge in case it would have to be evacuated. In some regions of the world that are particularly exposed to extreme environmental strains (e.g. typhoons), governmental security regulations require evacuation of personnel onboard production sites during periods when the personnel are apt to be exposed to typhoons. This is the case in the Gulf of Mexico and in Chinese waters, among other places.
The system according to the invention implies that such evacuation could be accomplished quickly and efficiently, by disconnecting the propulsion/support vessel from the barge and moving it to a safe area of the ocean. Compared to evacuation by helicopter, a such alternative evacuation of personnel would involve considerable advantages such as the shortest possible shutdown, a high degree of safety of personnel, no need for helicopter transport, etc.
Since the propulsion/support vessel is positioned in a protected area relative to the production/drilling site and capable of being very rapidly disconnected from the barge, the various governmental authorities would tend to be sympathetic as to accepting building the propulsion/support vessel in accordance with marine rules and regulations, which would also mean considerable additional economical advantages. The designation xe2x80x9cpropulsion/support vesselxe2x80x9d as used herein, is a general term applicable to any vessel reflecting the multipurpose aspect of the system according to the invention.
The modular approach according the invention implies additional advantages enhancing flexibility or versatility in a very positive manner and reducing the total cost level. The following, among other things, can be mentioned:
The propulsion/support vessel can perform additional finctions at the field, such as preparedness, fire prevention, oil skimming, assistance related to the mooring of tankers loading oil, ROV operations, etc. When used in the Gulf of Mexico, the propulsion/support vessel could take care of transport of personnel to and from the field. Such additional functions, as a general rule, is contemplated to last for a relatively short period of time, such that the living quarter function could be maintained.
In some regions of the world there is limited access to docking capacity for large ships. By using the modular system according to the invention, barge hull dimensions could more easily be selected to fit within local limitations. This property would also permit the vessels of the floating structure according to the invention to be moved into regions with limited physical accessibility, such as via the rivers into the Caspian Sea. This means higher flexibility in connection with the building and equipment of the barge, and would also be an advantage in connection with future maintenance operations, etc.
The connection portion between barge and propulsion/support vessel would also be standardized, resulting in flexibility with regard to alternating vessels, etc. This property also opens a possibility of vessel co-operation between several field operators operating the same type of units primarily within the same geographical region.
The crux of the invention is the possibility of interconnecting vessel units having widely different purposes/properties which, through a synergetic effect results in accomplishments beyond the mere additive effect of the properties of the individual vessels. Depending on what types of vessels are combined, the totality of the vessel-properties can be changed.
The main units and their properties that when combined will provide such synergy effect would be:
Barge units equipped for operations such as drilling, production of hydrocarbons, pipe laying, single-point buoy mooring loading, storing of hydrocarbons;
barge units having mooring equipment and interconnected depending on the intended operations;
barge units adapted to receive self-floating system modules for assembling desired equipment;
system modules to be received in the barge unit;
vessels having propulsion machinery for connection to a barge unit or interconnection of barge units;
a high DP class can be imparted to a barge unit or barge unit assembly by interconnecting several propulsion/support vessels, that individually have lower DP class than the one desired in the particular case;
the propulsion/support vessels that are interconnected to barge units are equipped for auxiliary functions and personnel accommodation;
modularized stern parts and bow parts to be connected according to needs;
interconnection in the open sea as opposed to in a harbor as is the usual way of interconnecting;
interconnection of vessels having widely different properties of use;
transverse dock for receiving system modules;
possibility of interconnecting vessels and accommodating self-floating system modules providing flexibility as to water depth, smaller vessels; and
modules having low draught can be transported/floated through shallow waters and then interconnected to perform operations in such waters (such as rivers in Russia and shallow parts of the Caspian Sea), while vessel combinations can naturally also be adapted for use in deep waters.